Browsing by Author "Uz, Yusuf Can"

Now showing 1 - 3 of 3

Analytical and numerical sensitivity analysis of constant temperature hot-wire anemometre
(Izmir Institute of Technology, 2014) Uz, Yusuf Can; Özkol, Ünver
Hot-wire anemometry (HWA) has been used for many years as a research tool in fluid mechanics. HWA consists of a wire sensor, a very fine element exposed to the fluid flow and of an electronic system, which performs the transformation of the sensor output into a useful electric signal. HWA is based on convective heat transfer from a heated wire which is placed into a fluid flow. The heat is generated inside the very fine wire owing to wire resistance when electrical current passes through it. Then, the wire will be subjected to heat losses by convection, conduction and radiation depending on the flow condition. To examine the theory of operation for the heated wire and plot the temperature distribution along it, energy balance for HWA is investigated by taking differential element of dx length of the filament. In order to understand static and dynamic characteristics of hot-wire, all kinds of heat transfer such as convection, conduction and radiation are taken into consideration. In present thesis, the static study starts to investigate influence of the sensor parameters on general behavior of the constant temperature hot-wire anemometer analytically and numerically at varying conditions. Most important part of this study is that the time dependent differential equation for the heated wire is solved to determine sensitivity of hot-wire by a perturbation method in the event of a harmonically changing heat transfer coefficient. Moreover, the influence of thin supporting wires, or copper plated wire ends, is evaluated to see the effects of them on sensitivity and heat dissipation to the prongs. Another important parameter for wire sensor is the aspect ratio (L/d). Aspect ratio affects the time constant, sensitivity and temperature distribution of heated wire; hence it needs to be examined. Also, effect of the various velocities on the temperature distribution and sensitivity along the hot-wire has been studied.
Citation - WoS: 2
Citation - Scopus: 2
Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry
(Sage Publications Ltd, 2023) Uz, Yusuf Can; Tanoglu, Metin; Tanoğlu, Metin
The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods.
Development and characterization of innovative fiber reinforced prepregs and their composites containing functional fillers
(Izmir Institute of Technology, 2021-07) Uz, Yusuf Can; Tanoğlu, Metin; Tanoğlu, Metin; Izmir Institute of Technology
This Ph.D. thesis aims to prepare laboratory-scale carbon fiber reinforced prepregs and improve the performance of their composites by incorporating functionalized single-wall carbon nanotubes (SWCNTs). The effect of nano-scale functional fillers on the characterization of prepregs and their composites was investigated to develop innovative materials for primary structures. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with the carboxyl (-COOH) group using acid treatment. The modified resin system containing 0.05, 0.1, and 0.2 wt. % F-SWCNTs were developed with novel multi-step dispersion techniques. FTIR spectroscopy was performed to identify new bonding groups formed after the covalent functionalization. Unidirectional carbon fiber reinforced prepregs with/without F-SWCNTs were prepared using a drum-type winding technique by utilizing the solvent-dip (solution impregnation) process. The effect of F‐SWCNTs on the curing process and kinetic parameters of the carbon fiber/epoxy-based prepregs were investigated using non‐isothermal DSC. The activation energy of the curing reaction was calculated by the isoconversional methods. Also, the new numerical approach called GMN was developed to determine the activation energy of the thermosetting materials. For the fabrication of prepreg-based composite laminates, the vacuum bag-only (VBO) method was performed. The fiber volume fractions of the CFRP samples changed between 55.3% and 50.16%. The mechanical and thermomechanical properties of prepreg-based CFRP composites with/without F-SWCNTs were investigated. The optimum mechanical properties of F-SWCNTs filled CFRP composite was achieved at 0.05 wt.% of F-SWCNTs. However, mechanical properties were decreased due to the addition of higher content of F-SWCNTs, in comparison with neat CFRP.